iframe-proxy | Sunbelt Computer Software

History

212 lines (187 loc) · 8.01 KB

Raw

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

158

159

160

161

162

163

164

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

183

184

185

186

187

188

189

190

191

192

193

194

195

196

197

198

199

200

201

202

203

204

205

206

207

208

209

210

211

212

module;

#ifndef _WIN32

#include <sys/types.h>

#include <sys/socket.h>

#include <netdb.h>

#include <unistd.h>

#include <poll.h>

#endif

export module mcpplibs.tinyhttps:platform;

import std;

// mcpplibs.tinyhttps:platform — the one place OS-specific networking quirks

// live. Everything else (socket.cppm, http.cppm…) stays portable and branches

// on `platform::is_windows` with `if constexpr`, never raw #ifdef.

// Sole concern today: hostname resolution on platforms where libc can't do it.

// A musl-static binary on Android/Termux can't resolve through getaddrinfo() —

// libc reads /etc/resolv.conf, but Android's /etc is read-only with no

// resolv.conf; Termux keeps its nameservers in $PREFIX/etc/resolv.conf, which

// libc never consults. So getaddrinfo stalls on a dead 127.0.0.1:53 and every

// HTTPS fetch (github, gitcode, anything) ends in "Connection failed". We read

// the relocatable resolv.conf ourselves and run a UDP DNS query. Self-contained:

// no shelling out to curl/getprop, no extra deps.

namespace mcpplibs::tinyhttps::platform {

// Compile-time platform flag for `if constexpr` at call sites.

export inline constexpr bool is_windows =

#ifdef _WIN32

true;

#else

false;

#endif

#ifndef _WIN32

namespace {

inline bool is_numeric_host(const char* host) {

// An IPv4/IPv6 literal is digits, dots, colons and hex letters only. This is

// a fast pre-filter; getaddrinfo(AI_NUMERICHOST) downstream is the real check.

if (host == nullptr || host[0] == '\0') return false;

for (const char* p = host; *p; ++p) {

char c = *p;

bool ok = (c >= '0' && c <= '9') || c == '.' || c == ':'

|| (c >= 'a' && c <= 'f') || (c >= 'A' && c <= 'F');

if (!ok) return false;

}

return true;

}

// Nameservers from the first readable resolv.conf, $PREFIX (Termux) first.

inline std::vector<std::string> resolv_nameservers() {

std::vector<std::string> servers;

std::vector<std::string> paths;

if (const char* prefix = std::getenv("PREFIX"); prefix && *prefix) {

paths.emplace_back(std::string(prefix) + "/etc/resolv.conf");

}

paths.emplace_back("/data/data/com.termux/files/usr/etc/resolv.conf");

paths.emplace_back("/etc/resolv.conf");

for (const auto& path : paths) {

std::ifstream f(path);

if (!f) continue;

std::string line;

while (std::getline(f, line)) {

if (auto hash = line.find('#'); hash != std::string::npos) line.erase(hash);

std::istringstream is(line);

std::string kw, val;

if ((is >> kw >> val) && kw == "nameserver" && !val.empty()) {

servers.push_back(val);

}

if (!servers.empty()) break;

}

return servers;

}

// Query one nameserver for A records of `host`. Returns dotted-quad IPv4s.

inline std::vector<std::string> dns_query_a(const std::string& server, const char* host, int timeoutMs) {

std::vector<std::string> ips;

unsigned char q[512];

size_t n = 0;

q[n++] = 0x12; q[n++] = 0x34; // id

q[n++] = 0x01; q[n++] = 0x00; // flags: recursion desired

q[n++] = 0x00; q[n++] = 0x01; // qdcount = 1

q[n++] = 0x00; q[n++] = 0x00; // ancount

q[n++] = 0x00; q[n++] = 0x00; // nscount

q[n++] = 0x00; q[n++] = 0x00; // arcount

for (const char* p = host; *p; ) { // qname: length-prefixed labels

const char* dot = p;

while (*dot && *dot != '.') ++dot;

size_t len = static_cast<size_t>(dot - p);

if (len == 0 || len > 63 || n + len + 1 >= sizeof(q)) return ips;

q[n++] = static_cast<unsigned char>(len);

for (size_t i = 0; i < len; ++i) q[n++] = static_cast<unsigned char>(p[i]);

p = (*dot == '.') ? dot + 1 : dot;

}

q[n++] = 0x00; // root label

q[n++] = 0x00; q[n++] = 0x01; // qtype A

q[n++] = 0x00; q[n++] = 0x01; // qclass IN

struct addrinfo hints{};

hints.ai_family = AF_INET;

hints.ai_socktype = SOCK_DGRAM;

hints.ai_flags = AI_NUMERICHOST;

struct addrinfo* sres = nullptr;

if (::getaddrinfo(server.c_str(), "53", &hints, &sres) != 0 || sres == nullptr) return ips;

int fd = ::socket(sres->ai_family, sres->ai_socktype, sres->ai_protocol);

if (fd < 0) { ::freeaddrinfo(sres); return ips; }

bool sent = ::sendto(fd, q, n, 0, sres->ai_addr, sres->ai_addrlen) == static_cast<ssize_t>(n);

::freeaddrinfo(sres);

if (!sent) { ::close(fd); return ips; }

struct pollfd pfd{};

pfd.fd = fd;

pfd.events = POLLIN;

if (::poll(&pfd, 1, timeoutMs) <= 0) { ::close(fd); return ips; }

unsigned char resp[1024];

ssize_t rn = ::recv(fd, resp, sizeof(resp), 0);

::close(fd);

if (rn < 12) return ips;

auto R = static_cast<size_t>(rn);

unsigned ancount = (static_cast<unsigned>(resp[6]) << 8) | resp[7];

size_t off = 12;

while (off < R && resp[off] != 0) off += resp[off] + 1; // question qname (no compression)

off += 1 + 4; // root label + qtype + qclass

for (unsigned a = 0; a < ancount && off + 12 <= R; ++a) {

if ((resp[off] & 0xc0) == 0xc0) { // compressed name pointer

off += 2;

} else {

while (off < R && resp[off] != 0) off += resp[off] + 1;

off += 1;

}

if (off + 10 > R) break;

unsigned type = (static_cast<unsigned>(resp[off]) << 8) | resp[off + 1];

unsigned rdlen = (static_cast<unsigned>(resp[off + 8]) << 8) | resp[off + 9];

off += 10;

if (off + rdlen > R) break;

if (type == 1 && rdlen == 4) {

ips.push_back(std::format("{}.{}.{}.{}",

resp[off], resp[off + 1], resp[off + 2], resp[off + 3]));

}

off += rdlen;

}

return ips;

}

} // anonymous namespace

#endif // !_WIN32

// True when libc's own resolver has a usable config (/etc/resolv.conf). When

// false, callers should prefer resolve_fallback() to avoid a multi-second stall

// on a dead 127.0.0.1:53. Always true on Windows (the OS resolver is reliable).

// Note: the bodies branch with #ifdef, not `if constexpr` — a non-template

// `if constexpr` still compiles its discarded branch, which would reference the

// POSIX-only helpers above that don't exist on Windows. Concentrating that

// preprocessor divergence here is exactly why this platform module exists; call

// sites elsewhere branch on `is_windows` with `if constexpr`.

export bool system_resolver_configured() {

#ifdef _WIN32

return true;

#else

std::error_code ec;

return std::filesystem::exists("/etc/resolv.conf", ec);

#endif

}

// Resolve a hostname to IPv4 literals WITHOUT relying on libc's resolver, by

// reading the system nameservers ($PREFIX/etc/resolv.conf on Termux) and doing

// a UDP DNS query. Returns {} on Windows, when no nameserver is configured, or

// on query failure. A numeric host is returned unchanged.

export std::vector<std::string> resolve_fallback([[maybe_unused]] const char* host,

[[maybe_unused]] int timeoutMs) {

#ifdef _WIN32

return {};

#else

if (is_numeric_host(host)) return { std::string(host) };

// Process-wide cache of successful resolutions. A single download performs

// several connects to the same host (HEAD probe, GET, redirect targets); on

// Termux each would otherwise re-run a UDP query to 8.8.8.8, and one dropped

// packet stalls the whole transfer. Cache once, reuse for the process.

static std::mutex cache_mutex;

static std::map<std::string, std::vector<std::string>> cache;

{

std::lock_guard<std::mutex> lock(cache_mutex);

if (auto it = cache.find(host); it != cache.end()) return it->second;

}

for (const auto& ns : resolv_nameservers()) {

auto got = dns_query_a(ns, host, timeoutMs);

if (!got.empty()) {

std::lock_guard<std::mutex> lock(cache_mutex);

cache.emplace(std::string(host), got);

return got;

}

return {};

#endif

}

} // namespace mcpplibs::tinyhttps::platform

Sunbelt Computer Software

PL/B Language Development and Support

Navigation Menu

Uh oh!

Sunbelt Computer Software

PL/B Language Development and Support

Uh oh!

FilesExpand file tree

platform.cppm

Latest commit

History

platform.cppm

File metadata and controls